1. Field of the Invention
The present invention relates to a filtration device that utilizes filtration media, such as activated carbon, to filter liquids, such as water. Particularly, the present invention relates to a filtration device that rotates a built in screw conveyor to cleanse the filtration media, in order to recover adsorption functions and filtration functions of the filtration media.
2. Description of the Related Art
If filtration devices are utilized for long periods of time, filtration media (filtration sand, activated carbon, and the like) within filtration tanks of the filtration devices become clogged. This prevents the performance of efficient filtration, and deteriorates the quality of filtered liquids, such as water. For this reason, clogging is eliminated by removing contaminants, which are attached to the filtration media. In order to perform operations efficiently, it is desirable that the process of removing the contaminants from the filtration media, that is, a cleansing process, be performed in a short amount of time with few steps. It is also desirable that the cleansing process be performed without taking up additional space. For these reasons, filtration sand cleansing devices (filtration media cleansing mechanisms) provided within filtration tanks have been considered. The provision of cleansing mechanisms within filtration tanks would enable efficient cleansing of filtration media in a short amount of time, without removing the filtration media from within the filtration tanks.
There are known filtration devices, as disclosed, for example, in Japanese Unexamined Utility Model Publication No. 63(1988)-98704, which have been developed in view of these points.
The filtration device disclosed in Japanese Unexamined Utility model Publication No. 63-98704 comprises an elevating pipe (cleansing tank) erected therein, and a spiral water elevator provided within the elevating pipe. During filtration, water is discharged by a water dispersing tube, which is within filtration sand. Processed water (filtered water), which has been filtered by passing through the filtration sand from below, is discharged above the filtration sand. During cleansing of the filtration sand, the spiral water elevator rotates and elevates the filtration sand, which has trapped contaminants, from the lower portion of the spiral water elevator. The contaminants are separated from the filtration sand by use of centrifugal force. The filtration sand is expelled through a filtration sand expulsion opening, which is provided in the upper portion of the elevating pipe. The filtration sand then returns to the interior of the filtration tank. The spiral water elevator is driven at its upper portion, and the lower end thereof is supported by a bearing.
In this conventional filtration device, the spiral water elevator is axially supported by the shaft of the spiral elevator being inserted into an aperture provided in the lower end of the tank. Therefore, if the portions of the shaft and the aperture that contact each other become worn, the shaft becomes loose in the aperture. As a result, there is a possibility that problems, such as smooth rotation of the spiral water elevator being prevented and water leaking, may occur.
If the spiral water elevator is supported at both the upper and lower ends thereof, rotational fluctuations and vibrations become less likely to occur. However, in an environment surrounded by filtration media, wear of the bearing cannot be prevented. In the case that the bearing becomes worn, there is a problem that the bearing cannot be easily repaired or replaced. In addition, filtration operations must be ceased during the repair or replacement.
The present invention has been developed in view of the foregoing points. It is an object of the present invention to provide a filtration device that automatically compensates for frictional wear of an axial support section of a screw conveyor when the axial support section becomes worn, without repairing or replacing worn parts, thereby maintaining stable performance over a long period of time.